Evaluation of a High-Hardness COMBO Medium and Frozen Algae forDaphnia magna

A new high-hardness (H-H) COMBO medium for long-term culturing and bioassay testing ofDaphnia magnawas evaluated in 21-day survival, growth, and reproduction studies. The COMBO medium originally designed for softwater daphnid species (i.e.,D. pulicaria) was modified for the hardwater speciesD. magna. This medium also allowed continuous culturing of a green algal food source for daphnids,Ankistrodesmus falcatus. After 12 generations of culturing in H-H COMBO medium, the mean fecundity was 128±12 (coefficient of VARIATION=9.4%). No significant observations of dead young, aborted eggs, or reduced antennas were made during the 6 months of continuous culturing. The no-observable-effect concentration (NOEC) for a reference toxicant standard, 3,4-dichloroaniline (3,4-DCA), was 8.3 μg/liter, which is similar to published values. These studies demonstrate that H-H COMBO is an acceptable medium for use for culturing and bioassay testing withD. magna.. Additional experiments using frozen aliquots ofA. falcatuswere conducted. Although mean fecundity (64±7) and adult length were significantly decreased from the values for daphnids fed fresh algae, the NOEC for 3,4-DCA was >25 μg/liter. The use of this alternative food source in bioassay testing appears promising, but further optimization of feeding rates is warranted.